Objectives: The primary aim was to establish normative values of isometric plantarflexor muscle strength in professional male rugby union players and compare forwards with backs. The secondary aims were to examine how individual playing position or age influences isometric plantarflexor strength.

Design: Cross-sectional.

Setting: Testing at professional rugby clubs.

Participants: 355 players (201 forwards and 154 backs) from 9 clubs in the English Premiership club competition.

Main outcome measures: Maximal unilateral isometric plantarflexion strength was measured, using a Fysiometer C-Station, in a seated position with a flexed knee and in maximal available dorsiflexion. Values are reported normalised to body mass and specific to playing position.

Results: Mean combined limb isometric plantarflexion strength for the group was 193.1 kg (SD 32) or 1.86 xBW. (SD 0.31). Forwards were significantly weaker than backs (forwards = 1.75xBW (SD 0.26), backs = 2.00xBW (SD 0.28) (p=<0.0001)). Age category revealed no influence on plantarflexor strength.

Conclusion: This study presents normative isometric plantarflexion strength values for professional male rugby union players. Forwards are typically relatively weaker than backs.

Keywords: Plantarflexor; Rugby; Soleus; Strength.

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